Classifying and identifying ferns

Scientists currently consider that New Zealand has approximately 230 species of fern in about 50 different genera. They are widely distributed throughout the country, including around 42 species that are found on all 3 main islands. These are ferns you may know and recognise. Their common names may be familiar to you (silver fern, hen and chickens fern) or perhaps you know their Māori name (ponga, mouku).

Botanists and other scientists document the characteristics of these ferns for classification and identification.

Fern characteristics

Ferns are quite simple structurally, and scientists begin by observing and documenting their sporangia, rhizomes and fronds.

The reproductive structures are the most important characteristic for classifying ferns. When you turn over a fern frond and look at the sporangia on the underside, you’ll quickly see that they are grouped together into various shapes and patterns. Sporangia can be grouped together into circles, elongated along the veins or arranged around the margin of the frond. There are numerous patterns and variations.

In addition, some sporangia are protected by a little membranous structure (an indusium), and others aren’t. These characteristics help us to sort out which family and which genus the fern belongs to.

For species, the vegetative characteristics become important. Is the rhizome creeping, vertical or erect? What is the shape of the frond? Is it highly divided or is it undivided? If it’s divided, to what degree is it divided? In addition, characteristics like whether there are hairs on the surface or not can also be useful.

Microscopic examination of spore shape and size and molecular analysis of fern DNA are two other techniques that are utilised.

Classification

Classification helps us put order into the world around us. Humans have been doing this for centuries. Classification provides a robust framework in which we can identify plants. In turn, this allows us to organise herbaria, retrieve information and undertake further study on plants.

The Linnean classification system places organisms within hierarchical groups that show their relationship to other organisms. Botanists and plant scientists rely on this system.

This is the classification for the hen and chickens fern:

Kingdom

Plantae

Division

Tracheophyta

Class

Polypodiopsida

Order

Polypodiales

Family

Aspleniaceae

Genus

Asplenium

Species

bulbiferum

Starting with the plant’s unique two-part Latin name (genus and species), the plant’s relationships to other plants is determined as you move up to family, order, class and division within the plant kingdom.

Identification

Every identified and classified organism has a unique two-part Latin name. The hen and chickens fern has the unique name Asplenium bulbiferum.

Two-part naming, also called binomial nomenclature, forms the basis of the modern classification system devised by Swedish botanist Carl Linnaeus in 1753. This orderly system gives each plant a ‘generic’ name (genus) and then a ‘specific’ name (species). In this system, the silver fern is known as Cyathea dealbata (the species name is descriptive meaning ‘white washed’), and the hen and chickens fern is known Asplenium bulbiferum (the species name is descriptive meaning ‘bearing bulbs’).

Today, the naming of plants is governed by a set of rules and recommendations produced by the International Code of Botanical Nomenclature (ICBN). Its intent is that each taxonomic group of plants has only one name that is accepted worldwide, thus reinforcing the value of a unique scientific name.

NATURE OF SCIENCE

Scientists need to communicate their ideas and share information in an accurate and clear manner. By using binomial nomenclature, scientists avoid confusion around common or multiple names given to organisms.

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